I finally got around to making the road tool for Criterium. The tool has two parts: a Java application that lets you paint roads on the 2D heightmap texture, and a Ogre-based tool that automatically converts a 2D path into a 3D mesh. The Ogre-tool queries the heightmap to get the height of the road, and performs smoothing so there are no discontinuous road segments. I've posted a screenshot below. Also, I've got my GIMP terrain shown in the screenshot. I generated it using random noise and the GIMP lightmap filter.